1. Field of the Invention
The invention is directed to a device for welding an accessory on a pipe by means of electrical heating elements intergrated in said accessory.
2. Description of the Related Art
The accessory welded to a pipe can serve as a reinforcement or for repairing a defective pipe. The segments can have, for example, a pipe socket for connecting other pipes to the pipe provided with the accessory. Finally, such an accessory can also be used for connecting two pipes. The heating element at the inner surfaces of the segments is heated by electrical current supplied from a welding device and liquefies the thermoplastic material between the circumferential surface of the pipe and the inner surface of the accessory. After cooling and solidification of the melted masses, a solid connection between the pipe and the accessory is realized.
Such accessories are known from DE 296 16 864 U1 wherein two segments are used which have corresponding heating elements and thus have identical electrical resistance relative to one another. In the known welding devices the two heating elements have always been electrically serially connected (serial connection) to the electrical current source of the corresponding welding device. This was achieved in that the electrical counter coupling members of the connecting lines coming from the welding device were contacted to two coupling members at the two segments of the accessory, but that the two further coupling members of the segments were contacted by a connector line to one another. This entails considerable disadvantages.
Since the heating elements are subjected sequentially to current flow, a relatively long welding time results until the required melting of the material at the contact location between the pipe and the accessory has occurred. Because of the duration of the welding time the heat generated by the heating element of the accessory has sufficient time to flow from the welding zone into the material of the accessory as well as that of the pipe. Therefore, it is required to expend more energy for the melting of the material in the known device in order to compensate the energy loss resulting from heat conduction. This means a greater energy expenditure in excess of that of the actual welding process which results in correspondingly high energy costs. Moreover, the migrating heat entails the risk of an insufficient welding of the segments of the accessory relative to one another as well as relative to the pipe.
The invention has the object to develop a reliable device of the kind mentioned above which produces flawless welding connections with minimal energy expenditure.